Cold Collisions, Quantum Degenerate Gases, Photoassociation, and Cold Molecules

Murray Holland

Ian W. M. Smith

The Chemistry of Cold Interstellar Cloud Cores Gas-Phase Reactive Collisions at Very Low Temperatures: Recent Experimental Advances and Perspectives The Study of Cold Collisions Using Ion Guides and Traps Theory of Low-Temperature Gas-Phase Reactions Molecular Spectroscopy at Low Temperatures: A High-Resolution Infrared Perspective The Production and Study of Ultra-Cold Molecular Ions Chemical Dynamics: Inside Superfluid Helium Nanodroplets at 0.37 K Kinematic Cooling of Molecules Manipulation of Molecules with Electric Fields Cold Collisions, Quantum Degenerate Gases, Photoassociation, and Cold Molecules.

Pierre Phou

Quantum degenerate molecular gases are of interest for the unique level of control they offer over chemical interactions and processes. To reach the quantum degenerate regime, these molecular gases must be cooled to ultracold temperatures, typically on the order of 100 nanoKelvins. Unlike atoms, with a few-level system that facilitates cooling, molecules represent a many-level system, which makes these temperatures experimentally difficult to achieve. As a result, experiments have turned to photoassociation and Feshbach resonance as shortcuts to form ultracold molecules from already ultracold atoms. Photoassociation and Feshbach resonance have been utilized to successfully create stable quantum degenerate molecules, but not on a routine basis, and only for a small range of molecular species. The primary focus of this thesis will be to study photoassociation and Feshbach resonance, and investigate possible routes to more efficient long-lived quantum degenerate molecule formation. We will also investigate realistic limiting conditions to open the possibility to more routine molecules, and to molecular species that are currently inaccessible. Overall, we find combined photoassociation and Feshbach resonance are viable schemes for efficiently creating quantum degenerate molecules, under realistic restrictions such as low laser intensity, narrow Feshbach resonance, and strong elastic collisions. As the techniques to create quantum degenerate molecules become more robust and experimentally available, the creation of colder, larger, and more long-lived samples will facilitate study of these molecules, and spur development into new applications.

Marius Lysebo

Johannes Hecker Denschlag

Changhyun Ryu, Du, X., Emek Yesilada +4 more

It has recently been demonstrated that quantum degenerate gases of very weakly bound molecules can be produced by atomic gases with Feshbach resonances. More strongly bound molecules can be produced with Raman photoassociation of a quantum gas, although this process has not yet been shown to produce a quantum degenerate molecular gas. In principle, Feshbach resonance and Raman photoassociation can be quantum-mechanically reversible, and lead to collective coherent phenomena such as Rabi cycling between an atomic and a molecular gas. However, such atom-molecular coherence has only partly been realized experimentally. Effects that may limit coherence include thermalizing elastic collisions, inelastic collisions, spontaneous Raman scattering, and pairing field formation. Here, we demonstrate a method that circumvents these limitations, based on Raman photoassociation of atoms in an optical lattice and driven into a Mott insulator state. We find that the Raman photoassociation transition is resolved into discrete lines corresponding to the quantized lattice site occupancies, and demonstrate that this provides a new method to accurately determine the distribution of site occupancies and the atom-molecule scattering length. Furthermore, we observe a Raman-induced oscillation of the central core of the gas, containing about 30% of the atoms, between an atomic and a molecular gas.